1. Field of the Invention
The invention relates to a hydrostatic transaxle including a motor casing incorporating a hydraulic motor for driving an axle drivingly connected to a pair of left and right steerable drive wheels, and a pair of steerable wheel support units attached onto opposite outer ends of the motor casing so as to steerably (i.e., horizontally rotatably) support the respective steerable drive wheels. Particularly, the invention relates to a structure of the hydrostatic transaxle adapted to a steering operation mechanism for turning the steerable drive wheels.
2. Related Art
There is a well-known conventional hydrostatic transaxle including a motor casing incorporating a hydraulic motor for driving an axle drivingly connected to a pair of left and right steerable drive wheels, wherein a pair of left and right steerable wheel support units are attached onto opposite outer ends of the motor casing so as to steerably support the respective steerable drive wheels. In each of the steerable wheel support units, a steerable casing supporting each of the steerable drive wheels is steerably (i.e., horizontally rotatably) connected to the motor casing. The hydrostatic transaxle is provided with a steering linkage including a simple tie rod connecting the steerable casings to each other for steering the left and right steerable drive wheels. Such a conventional hydrostatic transaxle is provided for various four-wheel drive working vehicles, e.g., an agriculture tractor, a riding lawn mower and construction machinery.
In the above-mentioned conventional hydrostatic transaxle, the tie rod requires a considerably large space (hereinafter, the space is referred to as “tie-rod arrangement space”) near the hydrostatic transaxle so as to be spanned between the left and right steerable casings, so that a space for arranging another member or device near the hydrostatic transaxle may be narrowed depending on where the tie rod is disposed.
JP 2005-35402A, for example, supposes the tie rod to be disposed (on the fore-and-aft proximate side of the hydrostatic transaxle) opposite to a pressure fluid pipe (on the fore-and-aft distal side of the hydrostatic transaxle) with respect to the hydrostatic transaxle so as to prevent the tie rod from interfering with the pressure fluid pipe. However, the tie rod still requires a laterally long tie-rod arrangement space near the hydrostatic transaxle so as to space other members and devices, such as another pressure fluid pipe (for supplying fluid to the hydraulic motor or for lubricating the hydrostatic transaxle) and/or a mechanical power transmission component (e.g., a propeller shaft), from the hydrostatic transaxle into the outside of the tie-rod arrangement space. That is, these members and devices surrounding the hydrostatic transaxle cannot be compactly arranged near the hydrostatic transaxle, thereby resulting in complex piping or mechanism, increased components and costs, inconvenience for assembly and maintenance, etc.